Reservoir Management in a Heterogeneous Clastic Reservoir - Zone 1 Prudhoe Bay Field

David D. Puls, Richard A. Levinson, Richard D. Newsom, Frank K. Paskvan, Robert S. Tye, Tak Sing Lo, John J. Lawrence, Masoud Haajizadeh

The basal section of the Ivishak Formation (Zone 1) is composed of a heterogeneous assemblage of reservoir sandstone with facies-dependent reservoir quality and dimensions. Non-reservoir rocks subdivide the reservoir vertically and create locally isolated compartments. Three phase fluid movement (gas/oil/water flood) adds to the complexity of reservoir management.

Successful exploitation of these reserves has required 1) a detailed characterization of the depositional architecture of the reservoir rocks, their interstitial shale barriers, and structure, 2) knowledge of the production characteristics of each type of reservoir and rate and pressure variations that each exhibits, and 3) management of water flood and gravity drainage production mechanisms as they impact oil production through time.

A series of geologic and engineering models were used to identify the most attractive in-fill targets and appropriate completion practices within a small area of Prudhoe Bay Field. Four horizontal wells were drilled to access reserves in moderate-quality, distributary mouth bar sands (13-25% porosity; 50-80 md K) where stand-off to gas was less than 60 feet. Low production rates in these wells (<1000 BOPD) were augmented by selective perforations in higher-quality, distributary channel sands (15-27% porosity; 165-195 md K). Hydraulic fracturing was used to enhance flow from heterogeneous mouth bar sands in conventional wells. In compartmentalized reservoirs, a balance between short-term, high production rates and long-term, added recovery benefits can be achieved by customizing dri ling and completion practices for the reservoir architecture encountered.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995